This invention relates to a corrugated board sheet transporting system in a printing line in which a plurality of printers are aligned straight in the direction of forwarding corrugated board sheets.
In a corrugated board carton making machine shown in FIG. 5, a multiplicity of corrugated board sheets S cut into a predetermined length are stacked and stocked in a sheet feeding unit 31 disposed at the upstream extremity, and the sheets S are delivered from the sheet feeding unit 31 one by one toward the downstream side. Each corrugated board sheet S is printed in predetermined different colors as it is fed successively through a sheet conveyor belt 32 to a first printing unit 33, through a sheet conveyor belt 36 to a second printing unit 37, through a sheet conveyor belt 38 to a third printing unit 39, and through a sheet conveyor belt 40 to a fourth printing unit 41. The thus printed corrugated board sheet S is forwarded successively to a creaser unit 42 to be creased there, to a slotter unit 43 to be slotted there and to a die-cutting unit 44 to be cut there.
The respective units 33, 37, 39, 41, 42, 43, 44 are designed to be separable and combinable with respect to one another. The printing units 33, 37, 39, 41 of the above units 33, 37, 39, 41, 42, 43, 44 are designed to be ascended in accordance with an order change and the like so as to allow a printing cylinder 34 and a press roll 35 constituting each printing unit to be spaced upward from the processing line O of the corrugated board sheet S. It should be noted here that intermediate transportation mechanisms 45, 46, 47, 48, which can be incorporated into the processing line O when the printing cylinders 34 and the press rolls 35 are spaced from the processing line O, are disposed below the printing units 33, 37, 39, 41, respectively, so that the sheets S can be forwarded by these mechanisms incorporated instead. Incidentally, the code FL means the floor level.
More specifically, for example, provided that the second printing unit 37 and the fourth printing unit 41 need not be used in accordance with an order change from four-color printing using the four printing units to a two-color printing using only two of the printing units, the second printing unit 37 and the fourth printing unit 41 are ascended to predetermined positions so as to space the printing cylinders 34 and press rolls 35 thereof from the processing line O, while the intermediate transportation mechanisms 46 and 48 locating below the corresponding press rolls 35 are incorporated into the processing line O, and then the processing line O is actuated. Thus, corrugated board sheets S can securely be forwarded by the intermediate transportation mechanisms 46, 48 even over the zones from where the second printing unit 37 and the fourth printing unit 41 are retracted.
By the way, in such printing unit described above, a large-scaled mechanism for ascending and descending the entire printing unit and the intermediate transportation mechanism is required in order changes, and such ascending/descending mechanism costs high, disadvantageously. In addition, the positioning accuracy of the intermediate transportation mechanism when incorporated into the processing line O is lowered depending on the state of engagement of gears for connecting the mechanism to a drive source and the like, disadvantageously.
Therefore, as shown in FIG. 6, there is proposed a printer in which only the printing cylinder thereof is designed to be ascendable. In the case where a plurality of the thus constituted printers are aligned straight in the direction of forwarding corrugated board sheets S, a sheet transporting system 53 of the illustrated constitution is interposed between a printer 51 locating upstream and another printer 52 locating downstream, with respect to the sheet forwarding direction. The sheet transporting system 53 consists of a lower feed belt unit 61 and an upper feed belt unit 63, and a corrugated board sheet S is adapted to be forwarded as it is held between these two feed belt units 61, 63. The lower feed belt unit 61 consists of a conveyor belt 62a locating upstream and another conveyor belt 62b locating downstream, with respect to the sheet forwarding direction, and the front extremity (upstream extremity) of the conveyor belt 62a and the rear extremity (downstream extremity) of the conveyor belt 62b are locating adjacent to press rolls 56 of the corresponding printer 51 or 52. Meanwhile, the upper feed belt unit 63 consists of a conveyor belt 64a locating upstream and another conveyor belt 64b locating downstream, with respect to the sheet forwarding direction, and these conveyor belts 64a, 64b are adapted to be able to move forward and backward with respect to the sheet forwarding direction. Incidentally, another sheet transporting system 53 of the same constitution is also disposed on the downstream side of the downstream printer 52.
Namely, in the upper feed belt unit 63, the conveyor belt 64a and the conveyor belt 64b are designed to be shiftable between standard positions A, i.e., the printers 51, 52 are in operation, where the rear extremity of the conveyor belt 64a and the front extremity of the conveyor belt 64b are moved closer to each other to allow the front extremity of the former and the rear extremity of the latter to locate at the positions closest to printing cylinders 55 of the corresponding printers 51, 52, respectively, as shown in FIG. 6, and advanced positions B, i.e. the downstream printer 52 is not in operation with the printing cylinder 55 thereof being ascended, where the conveyor belts 64a, 64b locating on each side of the printer 52 are advanced toward the ascended printing cylinder 55 thereof.
In the thus constituted sheet transporting system 53, for example, if the conveyor belts 64a, 64b locating on each side of the printer 52 are shifted to the advanced position, as shown in FIG. 7, when the printing cylinder 55 of the printer 52 is ascended to allow the printer 52 to assume a resting posture, corrugated board sheets S can be forwarded by the belts 64a, 64b at the position from where the printer 52 is retracted.
However, if the printing operation of the printer 52 is interrupted so as to ascend the cylinder 55 thereof for artwork replacement under the state where the printer 51 is performing printing operation, an extremity-to-extremity distance x is formed between these conveyor belts 64a, 64b locating at the advanced position with respect to the printing cylinder 55 of the printer 52; whereas another extremity-to-extremity distance y is formed between the conveyor belts 64a, 64b locating between the printers 51, 52. More specifically, since the downstream conveyor belt 64b is shifted to be spaced from the upstream conveyor belt 64a locating at the standard position in the sheet transporting system 53 disposed between these two printers 51, 52, the distance y becomes longer if the distance x is tried to be made shorter, whereas the distance x becomes longer if the distance y is tried to be made shorter. As described above, such extremity-to-extremity distance x or y is inevitably formed between the conveyor belts 64a, 64b locating at the advanced position, or between one locating at the standard position and the other locating at the advanced position respectively, so that the corrugated board sheet S cannot be held stably over such zones corresponding to the distances x and y to allow the sheet S to flirt, and thus corrugated board sheets S tend to fail to be forwarded securely and stably.
The present invention is proposed in view of the problems described above and in order to solve them suitably, and it is an objective of the invention to provide a corrugated board sheet transporting system in a printing line which is designed to carry out stable and secured transportation of corrugated board sheets even if the printing cylinder of a printer is ascended.